This invention relates to flight simulation in general and more particularly to an improved G seat system.
It is well known that one of the factors contributing to man's analysis of the acceleration profiles he is subjected to is his assessment of body motion and pressure sensation. In the case of the seated subject such as the pilot of an aircraft or the operator of a surface-based vehicle, this analysis is conducted normally while the subject is seated and is based on body excursion within the seat and pressure sensations arising from seat/body forces as perceived by the pressure sensitive neural receptors located in the buttocks area.
In the past, simulation efforts requiring the capability of inducing a sensation of motion as an informational cue have approached the problem in terms of large motion systems capable of subjecting not only the subject, but his immediate environment (cabin, cockpit, etc.) to motion profiles, the conceptual origins of which are founded on various philosophies concerning the manner in which to impart motion sensation, under very constrained means, via stimulating the semi-circular canals of the inner ear.
This approach is aimed primarily at providing informational cues via the inner ear; consequential bodily motion within the seat and buttock pressure variation are second order by-products of reduced magnitude and usefulness.
In some cases, depending upon the type of motion system drive philosphy employed, the second order effects are less than useful, in fact erroneous.
Basic G seats have been developed to emphasize the above-mentioned second order effects and make use of this source of motion-oriented information transfer. For example, see U.S. Pat. Nos. 3,270,440 and 3,097,436. These G seats use the bladder or air cell approach wherein the seat pan and seat back are divided into a number of individually controlled motion cells, the pressure of each being separately controlled to provide a means of moving the body within the seat frame. Side cushions composed of a number of cells are sometimes employed to provide outside thigh pressure inducing a sense of lateral acceleration or roll-orientation. Actuator controlled seat belts and shoulder strap harness complete the complement of motion cue inducing mechanisms. The neural receptor augmented G seat system of the present invention embodies and builds upon this very approach.
A cursory inspection of the above approach can lead to the basically erroneous assumption that both motion cue sources, body excursion within the seat and buttocks pressure sensation, are employed advantageously with the air cell or bladder approach; both sources of motion sensation are employed but not advantageously. In fact the two cue sources are in direct disagreement with one another.
Consider the case of the seated subject being accelerated upwards (acceleration vector directed from buttocks towards head). Under this condition, the subject should settle in his seat; his buttocks should assume a lower position with respect to the arm rests, for instance, than that normally experienced under at-rest, one G conditions. Simultaneously, the increased inertial loading on the upper torso is transmitted to the seat via the buttocks and increased pressure, particularly in the area of the flesh trapped between the seat and the ischial tuberosity bone structure, should be experienced. Similar flesh pressure increases under the ischial region are noted in the at-rest one G condition when a hard seat is chosen over a soft seat. The soft seat conforms more readily to buttock shape and lessens pressure concentrations under the tuberosities. A hard seat which does not conform so readily to buttocks shape increases flesh pressure under the tuberosity protrusions. Therefore, in the acceleration case under consideration, the subject may feel that the seat has become "harder."
Now consider the responses available with the air cells or bladder G seat when it is desired to simulate the above acceleration. In order to cause the subject to settle in his seat, the air bladder pressure is initially reduced resulting in the desired body excursion of settling deeper in the seat. However the air cells or bladders change shape under the pressure reduction and become more pliable and consequently fit the natural form of the buttock more precisely thereby relieving flesh pressure on the tuberosity region. As described above, increased tuberosity region pressure, not decreased pressure, is desired in this situation.
Likewise, consider the opposite maneuver when the induced acceleration is downward (from head towards buttocks). This maneuver might be characterized by the body/seat motion resulting when aircraft drop in air pockets or when a pilot goes "over the top" in an outside loop. The body should lift in the seat and inertial loading of the upper torso should cause flesh pressure in the tuberosity region to decrease. The simulation of this maneuver requires that the seat air cells be inflated to cause the body to be lifted in the seat. The inflation process causes the air cells to become less pliable, more firm, and the surface of the seat does not match as closely the natural form of the buttock resting upon it thereby increasing, rather than decreasing, the flesh pressure in the tuberosity region.
The above examples demonstrate the shortcomings of present air cell or bladder G seat systems. The rationable used in the above-described body/seat/pressure maneuvers; may be extended to other acceleration maneuvers however, the resultant seat response shortcomings are also present.